Electron tube



June 7, 1960 H. HILDEBRANDT ETAL 2,939,989

ELECTRON was Filed June 23, 1958 INVENTOR HARTIIUT HILDEBRANDT ALBERT F. W. STEGKE A. AGENT nited States Patent ELECTRON TUBE Hartnrut Hildebrandt, Hamburg, and Albert Fritz Willieim Stecker, Hamburg-Lockstedt, Germany, assignors to North American Philips Company Inc, New York, N.Y., a corporation of Delaware Filed June 23, 1958, Ser. No. 743,547 Claims priority, application Germany July 17, 1957 3 Claims. (Cl. 313-261) This invention relates to electron tubes in which the electrodes are supported by means of two insulating discs preferably made of mica, steps being taken to reduce microphonic disturbances.

The invention is based on recognition of the fact that the microphonic disturbances are mainly due to transverse deviations of the grid supporting rods. The disturbances are strongest when the deviations of the supporting rods are largest, that is to say, at a low natural frequency of the rods. The natural frequency is materially lower if the rods are supported at one end only. Consequently, the microphonic disturbance is increased if the supporting rods have some play in the apertures of the insulating supporting members. However, a certain amount of play is generally necessary to allow for the expansion of the supporting rods. I

According to the invention the microphonic disturbance is reduced in that both ends of the grid supporting rod connected to an electrode lead and one end of the other supporting rod are accommodated in apertures of the insulating supporting members without play, while the other end of this other supporting rod passes through the insulating member with a certain amount of clearance.

Thus, according to the invention, one end of the supporting rod not connected to an electrode lead is arranged in a Wide aperture of the insulating member while the other supporting rod ends are accommodated in small exactly fitting apertures. Alternatively, all the apertures in the insulating members can be made equal so that the supporting rods fit in the apertures with a certain amount of clearance, the supporting rod ends which must be rigidly secured being flattened.

According to the invention the necessary play of one end of one supporting rod can be readily determined from the diameter of the supporting rod and the acceleration forces which can occur. In tubes of a certain type, it was found that the play must be, for example, microns when the supporting rod diameter is 750 microns and the mechanical acceleration is 0.1 g, whether 3 is the acceleration of gravity. Generally, it is preferable to use a play of about 1% to 3% of the supporting rod diameter.

The effect of the invention will be illustrated with reference to a drawing.

In the drawing, which for the sake of simplicity shows only a grid secured between two mica members, the remaining electrodes of conventional construction being omitted, a grid wire 9 is secured to two supporting rods 1 and 2 which are secured in insulating discs 3 and 4. The supporting rod 2 is connected to an electrode lead 5 and flattened at the ends 7 and 8, so that it is held in the members 4 and 3 without play. The supporting rod 1, which is not connected to an electrode lead, is also flattened at 6 and secured without play, however, in accordance with the invention, the other end passes with a certain amount of play through an aperture 10 of the insulating member 3.

Hence the two supporting rods 1 and 2 have different natural frequencies for mechanical vibrations. An oscillation of the rod 2 is transmitted to the rod 1 through the coupling turns 9, however, there can be no common resonance, so that the oscillation is damped.

The deflection of the free end of the supporting rod 1, however, is restricted to 10 microns, so that the rod 1 strikes the ends of the aperture 10 and consequently the oscillation is clamped with the result that the resonance cannot be increased and the amplitude remains very small.

Experience has shown, that this effect occurs also if in the normal position the free end engages the edge of the aperture 10 since the slightest movement is sufficient to disengage this rod end from the edge of the aperture. Experiments have shown that any resonance deviations which occur are invariably damped.

Tests of a triode of conventional construction have shown, for example, that at a mechanical impact of 0.033 g an interference voltage is l/,u.v. is produced by the control grid, inter alia owing to the fact that the supporting rods of this grid have an appreciable amount of play in the mica members. It has been found that the steps in accordance with the invention reduce the interference voltage by a factor 4.

What is claimed is:

1. An electron discharge tube comprising at least one electrode, a pair of spaced, substantially parallel support rods to which said electrode is secured one of said rods having a terminal connection at one end thereof, a pair of spaced insulating members, said support rod having said terminal connection extending through and closely interfitting with each of one set of aligned apertures in said insulating members, the other of said support rods extending through another set of aligned apertures in said insulating members, said latter support rod interfitting closely with the aperture in one of said insulating members and passing through the aperture in the other of said insulating members with substantial clearance to allow movement of said support rod in said latter aperture.

2. An electron discharge tube as claimed in claim 1 in which the clearance between said latter support rod and said latter aperture exceeds the diameter of said rod by about 1 to 3%.

3. An electron discharge tube as claimed in claim 2 in which the portions of the rods passing through the apertures in the insulating members without clearance are flattened.

References Cited in the file of this patent UNITED STATES PATENTS 1,869,568 Krahl Aug. 2, 1932 

